The present invention relates to inlets for fluid tanks such as vehicle fuel tanks. In particular, the present invention relates to an anti-siphon inlet for a fluid tank such as a vehicle fuel tank.
The theft of fuel by siphoning from the fuel tanks of vehicles, and in particular commercial road vehicles, is a recognized problem. It is conventional to fit vehicles with a lockable fuel tank filler cap to prevent unauthorized access to the tank inlet. However, since the fuel filler cap is accessible it is vulnerable to tampering and can often be forced open by the determined thief. In addition, it is not always practical to fit a vehicle with a lockable fuel filler cap.
This problem has been addressed in the prior art by provision of a fluid tank inlet pipe incorporating structure to prevent insertion of a siphon tube into the tank.
For example, U.S. Pat. No. 3,951,297 discloses an anti-siphon fluid tank inlet assembly comprising a tubular inlet body which in use is secured to the normal tank inlet so that its distal end extends a short distance into the tank. The tubular inlet is designed to receive a conventional fuel dispensing nozzle. A conically-shaped guard member is provided at the open distal end of the tubular inlet so that an annular gap is defined between the conical member and the interior of the tubular body to allow fuel to flow from the dispenser nozzle into the tank. Breather holes are provided in the tubular inlet adjacent the tank inlet to allow the escape of air/gas from the tank as it is filled. The conical guard member is provided to prevent insertion of a siphon tube through the tubular inlet and into the tank below. A problem with this simple device is that it is still possible to siphon fuel from the tank when the fuel level is above the height of the distal end of the tubular inlet. Although the tubular body may only extend a relatively short distance into the tank, for instance of the order of 20 cm, this can nevertheless leave exposed a significant volume of fuel.
The above problem is addressed by anti-siphon inlet assemblies provided with a float valve as, for instance, disclosed in the applicant's co-pending GB patent application number GB 0 322 594. This has a float valve provided at the inner (distal) end of an inlet pipe. The float valve comprises a ball float retained in an apertured float chamber (or cage) and which seats against a valve seat defined at the end of the inlet pipe when the fuel level in the tank is above the end of the inlet pipe to thereby prevent fuel flow back through the pipe. A grill is fitted in the inlet pipe above the valve seat to prevent a siphon tube from being used to force the ball valve away from its seat. If the fuel level in the tank lies below the end of the inlet pipe, the ball valve will simply drop away from its seat allowing fuel flow through the apertures in the float chamber. Nevertheless, the grill will prevent insertion of a siphon tube into the fuel. When the fuel level is above the end of the inlet pipe, fuel can still flow through the float valve under pressure from the dispensing nozzle. With this assembly only fuel which may be present within the inlet pipe itself can be siphoned. Breather holes are provided in the inlet pipe towards the upper end of the pipe at the inlet to the tank, but at a height which will typically be above the maximum filling level of the tank.
Further examples of anti-siphon inlet assemblies provided with a float valve are disclosed in U.S. Pat. No. 1,995,007 and French Patent FR2534888.
In some cases, however, it may be possible to insert an elongate rigid member, such as a stiff length of wire, into the inlet assembly and through the grill protecting the float valve assembly in order to push the float member away from its seat. If this is done, it could then be possible to siphon off any fuel at a level above the level of the grill within the inlet pipe.